This invention relates generally to thermal protectors for current carrying circuits such as miniature thermostats, miniature circuit breakers and the like using bimetallic actuating assemblies and more particularly to a miniature thermal protector with a precalibrated automatic resetting bimetallic actuating assembly adapted for various applications, equipment and uses which require protection against abnormal changes in ambient temperature.
Valuable equipment and assemblies such as motors of various types, equipment with motors therein such as vacuum cleaners, automotive accessories, florescent lighting and HID ballasts, lighting fixtures, and other equipment and assemblies including, solenoids and PC boards and the like, require protection against overheating and against abnormal changes in the ambient temperature for any reason at the location where the equipment or assemblies are in operation.
Miniature thermostats using bimetallic actuating assemblies in which the current passing through the thermostat also passes through the bimetallic element are presently known and available in the commercial marketplace, for this purpose, such as the TI 7AM Thermal Protector manufactured and sold by Texas Instruments Incorporated.
These known thermal protectors are characterized by the fact that the bimetallic elements are affixed or attached in the bimetallic assemblies by welding to one of the terminals of the current carrying circuit and cantilevered so that a contact, also generally welded to the bimetallic element at the end remote from the welded or affixed end, is adapted under the conventional snap acting operation of the bimetallic element to move into and out of engagement with a stationary contact on the opposite terminal of the current carrying circuit.
In these miniature thermostats, an insulating material is sandwiched between the bimetallic element and the terminal carrying the stationary contact to enable these thermostats to be manufactured or fabricated in the smallest possible size and with the least number of parts so they can be manufactured and assembled on modern production equipment, accurately and cheaply and in quantities to meet the increasing commercial demand for such protective devices.
However, these known thermal protectors develop production problems because of the various stresses which are likely to occur, first, during the welding or affixing of the contact to the bimetallic element, and second, during the welding or affixing of the bimetallic element into assembled position in the thermal protector.
To overcome this problem, the manufacturers of the known thermal protectors recalibrate the bimetallic element and/or the bimetallic assembly in an effort to reset the thermal protector so they operate within the specified temperature rating for each particular size, current operating parameters and other limitations for the given thermal protector. However, even this recalibration technique does not achieve the desired accuracy required in the commercial marketplace.
The thermal protectors in accordance with the present invention overcome these production and other problems by providing an improved structure and operation such that the current in the current carrying circuit in which the thermal protector is connected does not flow through the bimetallic element. Further, the bimetallic element which is freely positioned in the thermal protector is operatively associated with and actuates an assembly having a contact movable therewith for coaction with a fixed contact to open and close the circuit to control the current passing through the thermal protector. This structure and operation eliminates the contact on the bimetallic element and the requirement for welding the bimetallic element into assembled position, and this eliminates the sources for the above mentioned prior art production problems.
In addition to overcoming the prior art production problems, the improved structure and operation for a thermal protector in accordance with the present invention also permits a wide range of actuating temperatures. First, because of the large number of variations for the bimetallic element which can now be achieved through the selection of the materials, the thickness, the shape and the curvature for the bimetallic element. Second, because the elements of the actuating assembly also can be modified through the selection of materials, thickness, width and length. Third, because of the operative coaction which can be obtained between the bimetallic element and the actuating assembly. Fourth, where the thermal protector cannot be further miniaturized, it permits the addition of a heater to achieve the predetermined actuating temperature for the bimetallic element. And last, when the parts and elements of the thermal protector in accordance with the present invention are assembled for operative relation with each other, they are automatically and accurately positioned for the required interrelationship between the bimetallic element and the leaf spring on the intermediate actuating element to achieve operation within the predetermined parameters for the given thermal protector, all of which will be more fully described below.